They argued patients should be allowed to take the drug if it helped reduce their pain or controlled symptoms of conditions like epilepsy.

Members of the Royal College of Nursing voted overwhelmingly in favour of lobbying the Government to change the law around the drug.

Nurses argued that painkillers such as morphine and fentanyl were both legal despite being from the same family as heroin, so cannabis should be treated no differently.

Legalising the drug would protect patients from disreputable dealers and prevent them being treated as criminals, they added.

Tracey Risebrow, a nurse from Suffolk, said: “Surely it is better to have patients using cannabis being monitored by health professionals able to pick up on any adverse effects quickly.

“It is inhumane to have people suffering when there is something that can help… We are making criminals out of people who only want to do what is best for their loved ones.”

Speaking at the union’s annual congress in Belfast, nurse Fallon Scaife said she had lost “the man I loved” to cannabis use but had since moved to a cancer ward and seen the benefits the drug had for patients.

Geoff Earle, from Edinburgh, added: “Our patients are often forced to use irresponsible dealers and risk prison sentences.”

Nurse Catherine Gault said she suffered from a chronic condition which may require treatment with cannabis in future, adding: “There is strong enough evidence to support the use of cannabis to treat pain. It would not be a recreational drug for me, it would add quality to my life.”

She said the move would protect vulnerable patients who were currently self-medicating with cannabis from illegal sources.

“It’s about protecting people who are actually breaking the law, but they are also putting themselves at risk because they don’t know the content of what they’re taking, they don’t know where the original source is from, they don’t know if people are putting something else in it,” she added.

Nurses voted in favour of the “complete decriminalisation” of the drug in all its forms, including “cannabis and cannabis resin”.

But the union’s chief said medical professionals would not advocate smoking the drug and making it available as a medicine would lead to fewer people smoking it.

As a Class B drug, cannabis cannot be prescribed, administered or supplied to the public.

Although the cannabis-based drug Sativex has been approved for MS sufferers, it is only available from specialist doctors in special circumstances and is not widely prescribed.

Over 40 countries, including Italy, Finland, Australia, Canada, Switzerland, Germany and half of the United States have decriminalised cannabis in some form.

Last month, the Royal College of Physicians – which represents 26,000 doctors in the UK – also called for the drug to be decriminalised, claiming the threat of jail meant addicts were put off seeking help.

Responding to the RCN news, Peter Carroll, of campaign group End Our Pain, said: “We welcome this bold and decisive move from the RCN. People who find relief from their symptoms by using medical cannabis should be treated as patients, not criminals.”

And Peter Reynolds, of cannabis law reform campaign group Clear, said: “This is recognition by the people we all turn to in our most difficult times that cannabis is an extremely valuable medicine which science now proves to be both efficacious and safe.”

But the Royal College of Psychiatrists urged caution. A spokesman said: “The legal status of cannabis and other drugs is a matter for government rather than doctors to decide. Cannabis carries significant mental health risks for some, including psychosis, depression and anxiety. We support medical use of NICE approved, cannabis products, following properly conducted independent research… Legalisation for recreational and medicinal use should be considered as distinct.”

Nurses also called for a a referendum on the final Brexit deal. The RCN passed a vote in favour of the move by 364 votes to 163 but is expected to consult more widely with members before campaigning.

The trade union was neutral in 2016 but is now the first to demand a second referendum on Brexit.

Chief executive Janet Davies said: “We can’t manage without our European nurses but they are already leaving. Even though we’re desperately trying to recruit, people aren’t coming from Europe in the number they used to.”